A small stepping motor which is used in a digital camera, a digital video camera, a slim ODD or the like is generally structured as shown in FIGS. 7(a) through 7(f). FIG. 7(a) is a plan view showing an end part of a motor, FIG. 7(b) is its front view, FIG. 7(c) is a side view showing an opposite-to-output side end part of the motor, FIG. 7(d) is an explanatory view showing an opposite-to-output side end face of a bearing holder, FIG. 7(e) is a cross-sectional view showing the bearing holder, and FIG. 7(f) is an explanatory view showing an output side end face of the bearing holder. The motor shown in FIGS. 7(a) through 7(f) includes a case 2′ into which a rotor and a coil are accommodated, a bearing 82′ which receives a shaft end of a rotation shaft of the rotor on one end side of the case 2′, a bearing holder 81′ which is provided with a bearing holding hole 810′ into which the bearing 82′ is inserted. Further, an opposite-to-output side of the bearing holder 81′ is disposed with a spring member 80′ which is provided with a plate spring part 83′ for urging the bearing 82′ within the bearing holding hole 810′ toward the rotation shaft (see, for example, Japanese Patent Laid-Open No. 2003-324892).
In the stepping motor structured as described above, the case 2′ may be formed in a cylindrical shape having a complete round shape when cut in a direction perpendicular to a motor axial line. Alternatively, the case 2′ may be formed in an elliptical shape in cross section like an example shown in FIG. 7(c) in order to reduce a thickness dimension in the direction perpendicular to the axial line direction of the motor (thickness dimension in a radial direction). In either case, the spring member 80′ is required to be fixed to the bearing holder 81′. Therefore, in the conventional examples, the spring member 80′ is formed with four hook parts 801′, 802′, 803′ and 804′ which are extended around roughly center portions of outer peripheral side faces of the bearing holder 81′ to be engaged with the bearing holder 81′. On the other hand, an output side end face 81b′ of the bearing holder 81′ is formed with recessed engaging parts 811′, 812′, 813′ and 814′ (slanted line regions in FIG. 7(f)), which are thin portions of the bearing holder 81′, so as to be engaged with the hook parts 801′, 802′, 803′ and 804′.
In the stepping motor as described above, when a thickness dimension in the direction perpendicular to the axial line direction of motor is reduced, for example, when the dimension “D” shown in FIG. 7(c) is reduced, the minimum width dimension “t” of a wall portion of the bearing holder 81′, which is formed between the recessed engaging parts 811′, 812′, 813′ and 814′ and the bearing holding hole 810′, becomes too narrow and thus the dimension of the bearing holding hole 810′ and accuracy of its shape are remarkably deteriorated. On the other hand, when the width dimensions of the recessed engaging parts 811′, 812′, 813′ and 814′ are narrowed, an engaging force of the spring member 80′ (hook parts 801′, 802′, 803′ and 804′) with the bearing holder 81′ is lowered. Further, when the entire bearing holder 81′ is formed of a thinner portion, a dimension for supporting the bearing 82′ in the axial line direction of the motor is shortened to cause the bearing 82′ to be inclined carelessly.